U.S. governmental regulations require that certain future automobiles that are powered by volatile fuel such as gasoline have their evaporative emission control systems equipped with on-board diagnostic capability for determining if a leak is present in a portion of the system which includes the fuel tank and the canister. One proposed response to that requirement is to connect a normally open solenoid valve in the canister vent, and to energize the solenoid when a diagnostic test is to be conducted. A certain vacuum is drawn in a portion of the system which includes the tank headspace and the canister, and with the canister and the tank headspace not being vented due to the closing of the canister vent, a certain loss of vacuum over a certain time will be deemed due to a leak. Loss of vacuum is detected by a transducer mounted on the fuel tank. Because of the nature of the construction of typical fuel tanks, a limit is imposed on the magnitude of vacuum that can be drawn. Too large a vacuum will result in deformation and render the measurement meaningless. In order to avoid this problem, a relatively costly vacuum transducer is required.
The present invention provides a solution to the problem which is significantly less costly. The key to the solution is a new and unique vacuum regulator/sensor which is disposed in the conduit between the canister purge solenoid and the canister. This vacuum regulator/sensor is like a vacuum regulator but with the inclusion of a switch that is used to provide a signal indicating the presence or the absence of a leak.
One aspect of the disclosed vacuum regulator/sensor that is especially unique is the manner in which the switch is embodied in it. Specifically, the movable valve element is a carbon-filled fluorosilicon that when seated on the associated valve seat, not only closes the valve seat, but also provides closure of the switch by bridging two electrical contacts that are embedded in the seat and that lead to corresponding terminals at the exterior of the vacuum regulator/sensor which provide the switch signal to external electronics.
Another aspect relates to the ability of the disclosed vacuum regulator/sensor to sense and indicate both positive and negative pressures relative to a reference (atmosphere), and this feature is useful in the performance of a multiple-part diagnostic test that takes into account the possibility that the ambient temperature might be sufficiently high enough to be volatilizing the liquid fuel at a rate that might otherwise impair the validity of the diagnostic test.
Further specific details of the construction and arrangements of the vacuum regulator/sensor and the system, and of the method of operation thereof, will be presented in the ensuing description.
Drawings accompany this disclosure and portray a presently preferred embodiment of the invention according to the best mode presently contemplated at this time for carrying out the invention.